The present invention relates to a measuring chamber for continuous flow-through of fluids which may contain radioactive isotopes. Such a chamber is part of a detection apparatus for detecting nuclide-specific gamma rays.
The discharge of exhaust air and gases as well as waste water from nuclear reactor plants have to be continuously monitored and supervised with regard to any radioactive contamination. The requisite measurement involves, for example, tapping and branching off a portion of the fluid to be supervised, and passing the branch stream through a measuring chamber which contains a suitable detector. The response time of the measuring device as a whole is the shorter, the shorter the residence time of the fluid in the chamber.
The known devices include a cylindrical measuring chamber having an inlet near the bottom for radial or tangential feed. The measuring fluid is discharged from the top and through an axial outlet. The top is preferably of conical configuration. A device of this type generally is disclosed e.g. by Gebauer in Atomwirtschaft, Mar. 19, 1977, page 150.
This known device is disadvantaged by the fact that the fluid molecules, gas or liquid, travel around the chamber along a very long circuitous path including many round trips around the axis and prior to discharge; their residence time is accordingly quite long. Moreover, it is practically impossible to avoid the formation of a stagnant flow zone which further increases the average residence time. The resulting long residence time is therefor directly responsible for a rather long delay in any indication that e.g. the radioactivity has increased. Moreover, the formation of eddies and stagnation zones contaminates the chamber and raises the zero or average level thereby simulating a higher radioactivity than actually present.